SMT Simultaneous Multi-Threading / Hyper-Threading
A physical CPU core appears as two (or more) "logical" cores — switches between threads when one stalls on a cache miss or branch misprediction.
Intel calls it Hyper-Threading (since Pentium 4, 2002). AMD calls it SMT. Gain on multi-thread workloads: typically 15–30 %. Downside: security holes (Spectre, MDS, Foreshadow) that have required SMT to be disabled in sensitive environments. Intel dropped Hyper-Threading on P-cores in Core Ultra 200 (2024) to free die area and simplify scheduling. AMD keeps SMT. P-state/C-state management interacts closely with SMT.